Hot melt adhesives are used in a wide variety of applications. In certain applications, relatively high bond strengths are required and polyurethane reactive (PUR) hot melt adhesives have been used due to the relatively high bond strengths they create. However, other characteristics of these adhesives provide various manufacturing challenges. For instance, PUR's react with atmosphere and must therefore be melted in a closed container. Accordingly, typical adhesive supply systems associated with PUR's include a closed melter unit that supplies heated adhesive to a gear pump. The adhesive is then supplied to a dispensing head through a heated hose to maintain the required temperature.
When PUR's are used in applications requiring relatively small quantities of adhesive per unit, such as the sealing of battery packs for personal computers, the residence time of the adhesive within the heated hose can exceed the “pot life” of the adhesive. The “pot life” is the maximum time at operating temperature before the adhesive starts to degrade, such as by charring and becoming more viscous. Exceeding the pot life of an adhesive can cause adhesive performance problems and increased maintenance.
It would be desirable to provide a dispensing system which does not require a large supply of adhesive to be maintained, and which is especially suited to the use of reactive hot melt adhesives. In addition, it would be desirable to provide a dispensing system as described above and which requires a minimum amount of space.